The purpose of this study is to investigate individual differences in children's sensitivity to others, and to examine sources of this variability. The study involves the naturalistic observation of children at a summer day camp, as well as interviews with each child to study his/her social inferential abilities. Specific issues investigated include (1) relations between aggressive and assertive behaviors and prosocial behaviors, (2) the dimensionality of prosocial behavior, specifically relations among different types of prosocial acts, (3) the possible mediating effects of role-taking and inferential abilities with regard to the relations between children's past interpersonal experiences and their later social behaviors, (4) sequential dependencies involving aggressive and prosocial behaviors, i.e., the facilitative or inhibitory (accelerating or decelerating) effects of expressed aggression with regard to later prosocial behavior. In addition, sex differences in aggression as a function of setting, mode of aggression, and sex of target are investigated.